An X-ray CT (computed tomography) of the inner structure of an object is a very powerful tool for the nondestructive observation. Since the development in early 1970's, it has found numerous applications in many fields of science, technology and medicine. Most of the methods which utilize the principal scheme of the CT are based on an X-ray absorption contrast. For example, a 3-dimensional medical image based on an X-ray absorption contrast considerably contributes to a medical diagnosing in addition to an ultrasonic image and an MRI (magnetic resonance imaging) in a medical field.
However, in recent years, X-ray imaging techniques have rapidly been developing and utilized a new kind of contrasts. One of the contrasts is a refraction contrast (i.e., the distribution of the X-ray intensity dependent on the refraction of the X-ray penetrated through an object).
In general, the refraction contrast may be any kind of the X-ray images with the intensity distribution thereof being a function of a refraction angle. Main advantages of the refraction contrast are the possibility to observe tiny cracks and deformations invisible in other types of contrasts and better sensitivity to the low Z materials. This is of great importance in medical imaging. The CT-reconstruction based on the refraction contrast has been expected to possess the same advantages.